Star Halos in M45 Image

[Knmurphy1]

Hello all,

just wondering if anyone knows what might be causing the star halos on the big stars in my M45 image. Processing them out doesn't seem to be an option. 
Even before the image is stretched I can see faint circles around them. 
I used a ZWO183C and (an old) Televue 76.

thanks guys.

Kevin 
 

[Elp]

It generally happens around bright stars especially during long exposures, if using filters this can also make it worse.

[vlaiv]

Some sort of internal reflection due to quantum nature of light.

Can be for example from camera front window. Although it is AR coated (anti reflex) - that just reduces and not completely eliminates reflections. Regular glass will reflect around 4% of light and AR coated brings that down to less than 1% - usually around 0.1% (again, if I'm not mistaken).

Very bright star will have many magnitudes higher brightness than say surrounding nebulosity - it can be even 10 mags of difference - which is x10000 more bright. 0.1% of x10000 is still x10 brighter than nebulosity and must show on image.

You can verify that it is reflection by the way this bright circle behaves - it will be offset from the center - further star is from the center - more offset (away from center) it will be. This halo is actually image of that star slightly defocused as light that reflected couple of times traveled larger distance and is no longer in focus.

[Knmurphy1]

Thanks for the replies guys. It was actually a modified EOS1100 D Canon camera I used, not the ZWO - my mistake. I might try my CLS-CCD filter to see if that reduces the halos.

[Elp]

That filter will also massively reduce the targets signal. No harm in trying but as mentioned they're bright stars, try it around brighter magnitude stars to see quicker results when testing.

Edited November 14, 2023 by Elp

[900SL]

Do you have a UV/IR filter on your modded camera?

Also, are you getting any dew forming on the lens?

[Bugdozer]

OK this isn't probably the answer but it might be... Is there any possibility there was some very thin cloud when you took this? I have a photo I took of Altair where it looked normal to my eyes but the outcome is pretty much like your picture - halo around Altair while dimmer stars are unaffected. Pictures taken later look normal, so the cloud had moved.